The present invention relates generally to systems and methods for allowing radiotelephones to acquire a control channel and, more particularly, to systems and methods for acquiring a control channel for selectively setting the number of entries in a history list, the content for the entries in the history list, and a threshold power level for a control channel.
A mobile radiotelephone system includes a base station serving one or more cells and a plurality of radiotelephones, which are commonly mobile radiotelephones or mobile stations. The radiotelephones communicate with the base station through two different types of channels. The first channel is a voice channel and is used to carry voice and other transmissions between the radiotelephone and a base station. The other type of channel is a control channel and is generally used by the radiotelephone in acquiring a voice channel and in obtaining other service from the base station. For instance, control channels are used by a radiotelephone to select a particular cell within a radiotelephone network and to acquire a voice channel. The control channels are also used for various other purposes.
In the United States, the predominate radiotelephone system for mobile radiotelephones, or cellular phones, is the Advanced Mobile Phone System (AMPS). AMPS is an analog cellular system deployed nationwide and currently uses a common set of 21 analog control channels from which a mobile radiotelephone can obtain service, receive pages for incoming calls, and originate outgoing calls. In general, the bandwidth available for AMPS is divided into an A-Band and a B-Band with these two bands being serviced by two different carriers. The A-Band has a range of channels in the 313 to 333 MHz bandwidth and the B-Band has a set of channels in the 334 to 354 MHz bandwidth. A mobile radiotelephone will typically be set for either the A-Band or the B-Band depending upon its carrier. Because of the fairly limited number of control channels in AMPS, a mobile radiotelephone can always ensure that a scan through these channels should result in finding an appropriate channel through which service may be obtained. If no channels are found, then the radiotelephone may assume that there is no service in the current area but continue to search periodically.
A new generation of mobile radio telephones is reflected in Telecommunications Industry Association (TIA) standard EIA/TIA IS-136. IS-136 capable mobile radiotelephones transmit and receive digital signals which have been multiplexed together in a time division multiple access (TDMA) system. These digital mobile radiotelephones offer a number of features not found in the pure analog mobile radiotelephones, such as short message service (SMS), voice and data privacy, a message waiting indicator (MWI), calling number identification (CNI), and circuit-switched data support. IS-136 capable digital phones are designed to operate both in the analog spectrum as well as in the purely digital spectrum of the 1900 MHz frequency bands. They provide seamless operation on both the AMPS analog cellular system as well as an IS-136 system.
A core component of the EIA/TIA standard IS-136 is the definition of a digital control channel (DCCH). The DCCH is a new control channel added to existing analog control channels (ACCs), analog voice channels (AVCs), and the digital traffic channels (DTCs) of a TDMA system. The DCCH enables many of the new functions and enhanced features of IS-136. In contrast to analog control channels, the DCCH may be placed on any channel in the frequency range of the mobile radiotelephone system and a radiotelephone network may offer a greater or lesser number of DCCHs than ACCs.
The detection and acquisition of a DCCH, however, is not as easy as the acquisition and detection of an ACC. As discussed above, the AMPS cellular network typically has twenty one control channels with these control channels being set at predefined frequencies. An AMPS cellular phone can quickly scan through the twenty one frequencies to find an ACC through which cellular service may be obtained. In contrast to an ACC, the DCCH may be located at any channel within the frequency range of the cellular carrier. Cellular networks, furthermore, may have differing numbers of DCCHs, with one network possibly having twenty one DCCHs while another neighboring network having thirty three DCCHs. Due to the uncertain number of DCCHs and their uncertain location within the available bandwidth, an IS-136 capable phone cannot quickly or easily perform a scan of the bandwidth to locate a suitable DCCH.
In light of the difficulty of scanning a multitude of channels in order to obtain cellular service, IS-136 phones are commonly provided with a xe2x80x9chistory listxe2x80x9d of channels. The history list is generated by the digital phone dynamically as the phone operates in a cellular environment. Typically, cellular carriers will utilize a common set of channels system-wide in which to place their DCCHs. A digital phone will build its history list of DCCHs by placing on the list those DCCHs through which the phone has obtained service with the first position on the list designated for the DCCH used most recently. When a digital phone attempts to locate a DCCH, the digital phone scans the entire list and removes from consideration those channels below a minimum threshold power level. Of the channels above the threshold, the radiotelephone selects the strongest channel available. A history list could theoretically contain any number of channels which the phone will scan for service, but a balance of the number of channels, the amount of time required to scan them, and the amount of memory required to store them will, as a practical matter, limit the number of DCCHs stored in the history list.
The factors of the time required to scan the channels and the maximum number of channels allowed in memory can greatly affect the performance of a digital cellular phone in a specific cellular network. For example, a digital cellular phone that stores only five channels in its history list operating in a system where the carrier has chosen to use twenty different DCCH channels for reuse across the system will only be effective at best five out of twenty different times. The five channels stored in the phone will preferably be channels that the user has acquired service on previously via different methods whereby the use of these five channels increases the user""s chance that one of them will be available. Nonetheless, by increasing the number of DCCHs stored in the history list, the digital phone increases its chances that it will find an available DCCH. For instance, if a digital phone increases the number of DCCHs stored in its history list from five to ten, then the odds that an available DCCH will be found is increased from approximately five out of twenty times to ten out of twenty times.
The structuring of the history list so that it contains the most recently used channels is not without its shortcomings. This type of history list works well when the user stays within commonly used cells of a cellular network or stays within just one cellular network. When the user enters other cells of the cellular network or enters another cellular network, the location of the DCCHs in these other cells or in this other network may be different from the locations of the DCCH for the cells within which the user typically travels. As a result, when the IS-136 capable phone attempts to locate a DCCH in one of these other cells or in another network, the IS-136 capable phone will likely find it difficult to obtain service using the DCCHs stored in its history list. The history list therefore provides its optimal functionality only when the user limits his or her movement to within a limited number of regularly used cells.
In addition to the problem of the uncertain locations of the DCCHs, a cellular carrier in one network may have a larger number of control channels than a cellular carrier in another network. For instance, one network may have twenty DCCHs while another network may have thirty DCCHs. For a phone that has five DCCHs stored in its history list, the phone has at best a five out of twenty chance of locating a DCCH in the first network and at best a five out of thirty chance of locating a DCCH in the second network. Consequently, the odds of a digital cellular phone acquiring service may be significantly affected by the number of DCCHs employed by a cellular carrier.
In view of the varying locations of DCCHs and the varying number of DCCHs within a cellular network, a given history list within a phone will have varying degrees of success as it travels from one cell to another cell and as it travels between networks. In view of these disparate results, a cellular carrier having a larger number of DCCHs may prefer that the history list contain a larger number of control channels. In such a network, the additional time needed to scan for a DCCH and the increased memory in the phone may be offset by the improved performance of the history list in permitting the digital cellular phone to obtain service. Other cellular carriers, in contrast, may employ a fewer number of DCCHs in their network and may desire just a minimal number of DCCHs in the history list. For these carriers, the additional scan time and additional amount of memory may prove to be overly burdensome on the radiotelephones and on network performance. It has therefore been a problem in balancing the competing desires of the cellular carriers in setting the number of DCCHs in the history list.
Another problem that digital cellular phones have encountered in using the DCCH is known as the xe2x80x9cfar away DCCHxe2x80x9d problem. The far away DCCH problem exists when a DCCH capable phone finds a channel for camping purposes when in fact the digital phone should not camp on that frequency. One instance in which this problem arises is when, due to geographic issues, a cell site which is very far away but is in the line of sight of the mobile radiotelephone has a signal strength sufficiently large that the mobile radiotelephone can use it to obtain service. With the far away problem, the radiotelephone is able to acquire service from a cell even though that radiotelephone is not presently located within that cell. Although the mobile radio telephone can set up a call on the far away cell site, the mobile radiotelephone would likely not be able to get a proper hand off to the next cell that radiotelephone enters since cellular systems typically only hand off from one cell site to an adjacent cell site. Because of the far away DCCH problem, digital cellular phones may encounter an dropped call scenario.
The dropped call scenario can be aggravated by the use of a xe2x80x9cneighbor listxe2x80x9d of channels. Each cell contains a neighbor list of DCCH channels which can assist the mobile station in reselecting from one cell site DCCH to the next cell site DCCH. This neighbor list of DCCHs is important since the DCCHs found in one cell are chosen to be different from DCCHs in neighboring cells in order to avoid interference. When a mobile radiotelephone enters another cell and attempts to reselect a DCCH on the neighbor list for service, the DCCHs on the neighbor list given to the mobile radiotelephone may very well not exist in the new cell and, as a result, the phone may not be able to reselect. Thus, the far away DCCH problem would impair the ability of a mobile radiotelephone to use a neighbor list to select a DCCH.
A further difficulty encountered by a digital phone occurs as a result of the different RF plans established by the various carriers. The carriers transmit their signals at different levels of power with some carriers transmitting their signals at higher power levels. For example, this scenario is prevalent in areas which employ the use of microcells. For those xe2x80x9chotterxe2x80x9d carriers that transmit at higher power levels, the strength of their transmitted signals at cell boundaries will be greater in comparison to those carriers which are not as hot. As a result, the RF plans for the xe2x80x9chotterxe2x80x9d carriers will call for a reselection to the next cell at power levels greater than those for the RF plans of other carriers. For instance, a relatively xe2x80x9chotxe2x80x9d carrier may design cells within its network so that a radiotelephone should initially acquire a DCCH via history list scanning only if the power level of the DCCH is above xe2x88x9270 dBm. Another carrier, in contrast, may perform its RF planning so that DCCH service should be initially acquired via history list scanning only if the initial DCCH power level is above xe2x88x9295 dBm. Despite the carriers"" RF plans, a radiotelephone may initially select another DCCH at a lower power level. The actual history list acquisition threshold within the mobile radiotelephone is set by the manufacturer and is often set without regard to the carrier""s RF planning. The power level threshold set by the manufacturer will likely therefore not be optimally set for a given cellular network. As an example, a manufacturer may set the history list acquisition threshold for a mobile radiotelephone at xe2x88x9285 dBm. For this phone and threshold, the phone will more easily find a DCCH in the network designed at the xe2x88x9270 dBm reselection power level in comparison to the network designed at the xe2x88x9295 dBm level. The discrepancy between a manufacturer""s set threshold and a carrier""s desired threshold is only compounded by the fact that different manufacturers of radiotelephones set their thresholds at different levels. The variations in the thresholds desired by the carriers coupled with the variations in the actual thresholds set by the manufacturers affect the quality of service among the IS-136 capable phones and among the cellular networks.
The present invention addresses the problems described above by providing systems and methods searching for a digital control channel. According to one aspect of the invention, an over-the-air programming teleservice (OAP) transfers data to a radiotelephone in response to a download event. The data transferred to the radiotelephone includes a search parameter that the radiotelephone stores within its database. The radiotelephone turns to the database for determining the manner in which to search for a digital control channel within a radiotelephone network. The search parameter may comprise any parameter influencing the search by the radiotelephone, but preferably comprises the number of entries in the radiotelephone""s history list, an entry for placement within the history list, and a threshold level for the digital control channel.
The invention advantageously allows a carrier to influence the manner in which its subscribing radiotelephones search for digital control channels. As a result, the radiotelephones can be programmed to have a desired number of entries in their history lists, with carriers employing a larger number of digital control channels being able to enlarge the history lists of their subscribing radiotelephones. With the ability of programming the content for the history list entries, carriers are able to increase the chance of a radiotelephone to locate and camp on a digital control channel. Also, the radiotelephones within a network can be programmed as a group or individually, which allows the carrier to ensure that its subscribers use the appropriate cellular network when roaming. By setting the threshold level, carriers can ensure that operations of their subscribing radiotelephones are optimally set for the RF planning of their networks. Consequently, the far away DCCH problem and problems associated with the history list are reduced.
Accordingly, it is an object of the present invention to provide systems and methods for acquiring and using a digital control channel that enables over-the-air programming of a radiotelephone""s search algorithm.
It is another object of the present invention to provide systems and methods for acquiring and using a control channel or traffic channel that allows the search algorithm of a radiotelephone to be optimally set.
It is a further object of the present invention to provide systems and methods for acquiring and using a control channel or traffic channel that allows programming of a radiotelephone""s history list.
It is yet another object of the present invention to provide systems and methods for acquiring and using a control channel or traffic channel that allows programming of a power level threshold.
It is yet a further object of the present invention to provide systems and methods for acquiring and using a control channel that allows programming of a number of entries in a history list.
It is still a further object of the present invention to provide systems and methods for searching for a digital control channel that allows programming of entries in a history list.
Other objects, features, and advantages of the present invention will become apparent with respect to the remainder of this document.